#9964: fix running test_xml_etree under -OO.

Lib/test/test_xml_etree.py

@@ -1835,6 +1835,10 @@ class CleanContext(object):
     checkwarnings = None
 
     def __init__(self, quiet=False):
+        if sys.flags.optimize >= 2:
+            # under -OO, doctests cannot be run and therefore not all warnings
+            # will be emitted
+            quiet = True
         deprecations = (
             # Search behaviour is broken if search path starts with "/".
             ("This search is broken in 1.3 and earlier, and will be fixed "